In an injector, as used e.g. in common rail systems, fuel injection into a combustion chamber of a cylinder of an internal combustion engine is controlled by an actuator. Such actuators can be implemented, for example, as stacks of piezoelectric crystals.
Injection can be controlled by allowing fuel to flow from a high-pressure region of the injector to a low-pressure region of the injector, e.g. via a control valve. The resultant pressure differences enable a nozzle of the injector to be opened so that fuel is injected into a combustion chamber. Such control of the opening and closing of the nozzle may take place by the actuator causing the spray hole or holes to open and/or close only indirectly, via pressure differences.
The problem now is that if, for example, a valve is opened between the high- and low-pressure region in order to bring about the pressure change necessary for opening the nozzle or more specifically a spray hole, pressure waves can propagate in the high-pressure region and/or in the low-pressure region. In addition, numerous other effects can influence the setting and change of the pressures in the high- and low-pressure region. In particular, even in the low-pressure region, uncontrolled and unpredictable gas inclusions may be present or be caused by pressure fluctuations which affect the pressure conditions. Such pressure changes can retroact on the valve, the actuator and other components involved in injection control.
Uncontrolled pressure conditions in the high-pressure region and/or in the low-pressure region affect the injection quantity, as the action of the actuator is transmitted by means of pressure changes via the fuel in the high- and/or in the low-pressure region to the mechanism which opens and closes the spray holes or nozzles for injection. Therefore, unless the pressure conditions are the same and precisely known for each injection, a given activation of the actuator will result in different injection quantities depending on the pressure conditions in the high- and/or low-pressure region. Of particular relevance here is the fact that, for a given activation of the actuator, different pressure conditions may result in different speeds and durations of opening of the spray holes or nozzles.